Vacuum cups are commonly employed as workpiece gripping elements to engage and transport workpieces in a manufacturing operation, to load and unload sheet metal parts into and out of a die, or to carry a part, such as an automobile windshield, to the vehicle to which it is to be installed.
Such vacuum cups generally employ a control apparatus for employing a vacuum to the vacuum cup. One such common design for the control apparatus is the use of a venturi passage in a body which is connected to a source of pressurized air. The air flow passes through the venturi passage and induces subatmospheric pressure in the throat of the venturi and in a passage connecting the venturi throat to the interior of the vacuum cup which induces a vacuum within the cup when the cup engages a workpiece surface. Earlier versions of such a vacuum cup control apparatus required that the air continually flow through the venturi passage in order to maintain vacuum in the cup since air at atmospheric pressure was free to flow back through the discharge vent once the air flow was stopped. Such venturi passages are loud, require a large amount of air to maintain the vacuum in the vacuum cup, and must continually operate to maintain vacuum.
Further developments led to the use of one way check valves between the vacuum cup and the venturi passage to seal the vacuum in the vacuum cup, thus allowing vacuum to be maintained within the vacuum cup once air flow is stopped from passing through the venturi passage. Such designs allow for air flow to be stopped but these designs may not compensate for small leaks or loss of vacuum which may occur between or within the vacuum cup and the workpiece. Therefore, the pressure within the vacuum cup must be continually monitored in conjunction with the air flow being intermittently engaged such that vacuum within the vacuum cup is maintained to secure the workpiece to the vacuum cup.
Other designs have utilized a vacuum pump to supply vacuum directly to the vacuum cup. To avoid having the vacuum continually operate, various sensors were developed wherein the sensors sense contact between the vacuum cup and the workpiece. An output signal from the sensor causes vacuum to be applied to the vacuum cup. Such systems typically involve program delays to allow for the vacuum to respond to the signal. In addition, such systems typically require a host of sensors as well as a multitude of programmable electronics which may become expensive and high maintenance items.
In addition, further designs have developed the use of mechanical valves within the vacuum cup. The valves typically utilize a spring biased piston head which directly engages the workpiece. The piston head recedes into the vacuum cup when engaged by the workpiece causing the valve to open. Vacuum is applied to the suction cup through the open valve thus securing the workpiece to the vacuum cup and holding the valve open. When pressurized air is actuated, the pressurized air flows through the open valve until the workpiece is no longer secured to the vacuum cup due to atmospheric pressure in the vacuum cup. The spring biased valve closes, and the piston head helps disengage the workpiece from the vacuum cup. Such mechanical valves require the piston head to directly engage the workpiece without much room for error in the positioning of the vacuum cup. In addition, each vacuum cup requires its own valve thus requiring the costly operation of replacing both the valve and the vacuum cup should the vacuum cup or valve become damaged. Also, such valves do not have the flexibility of utilizing different style vacuum cups with the same valve for different workpiece configurations or applications.
Thus, it would be desirable to provide a vacuum cup actuator that only provides vacuum to the vacuum cup when needed while still accommodating for minor linkages occurring in the vacuum cup. It would also be desirable to provide a vacuum cup actuator that provided immediate vacuum to the vacuum cup so as to eliminate delays for vacuum response. In addition, it would also be desirable to provide a vacuum cup actuator that does not require close positioning tolerances of the automation utilized to manipulate the position of the vacuum cup with respect to the workpiece.